Basic question, 3 phase terminology...

[charlie]

. . . the power company linemen . . take no particular pains to provide either a clockwise or counterclockwise rotation to a building . . .

Do your linemen have to keep track of which conductors are "A" phase all the way from the poco generator through the substations through the last xfmr so that "A" is always "A"?

To answer the first question, you are correct. However, we use a phase rotation meter to verify that the rotation is correct if we rebuild or replace a bank of transformers. I assume that other electric utilities have the same practice.

The second question is more complicated. We do indeed keep track of A?, B?, and C? from the substations so that we can balance the loads on the primary phases from the substation (I don't know much about transmission line engineering). Also, we always put the lighter (the one that is center tap connected to the neutral) of an open delta bank on the leading phase. It is not the linemen that do this but the engineers specify the phasing on the work request drawing and specify which transformer goes on which phase. This information is kept on our AM/FM system (automated mapping and facilities mapping). Again, with the advent of AM/FM systems, I assume that other electric utilities have the same practice.

 

[dicklaxt]

Standards in fabrication of Swgr,MCC,s etc is left to right A-B-C and front to back A-B-C. I have always applied that to what ever.

dick

 

[don_resqcapt19]

The power company may give you a counter-clockwise rotation while the premises next door may have a clock-wise rotation. And your "A" phase may be your neighbor's "C" phase. That is what I have seen.

Any of the POCO reps disagree? On a new service/bulding, do your linemen worry about rotation or any particular termination on the xfmr being "A" phase?

Gary,
While what you say about the utility is correct, it can result in a code violation. 408.3(E), 409.102(B) and 430.97(B) all call for the phase arrangement to be "A, B, C from front to back, top to bottom, or left to right, as viewed from the front". I read this as requiring a clockwise rotation when I hook my phase meter leads in the correct order from top to bottom or left to right. I am not saying that my "A" phase has to be the same as your "A" phase, just that the rotation must be the same. ABC=BCA=CAB All of these would be in compliance as they all provide the same rotation.

 

[charlie]

. . . I read this as requiring a clockwise rotation . . .

Sorry Don, I don't read that at all. I would hate to be the electrical contractor with a new 3000 ampere switchgear that was just energized and find the rotation was reversed. Now you would be required to reverse two phases if you couldn't talk the serving electric utility into reversing theirs (fat chance).

 

[don_resqcapt19]

Charlie,
If that is not what it means, then it has no meaning and should be removed from the code. As has been pointed out in this thread, the terms A, B and C have no real meaning. If the rotation is not being specified by these sections, then what would be the purpose of the code sections?

 

[charlie]

. . . If the rotation is not being specified by these sections, then what would be the purpose of the code sections?

To have a question that can be used on exams? Seriously though, I do not know. To my knowledge, there is no good reason to keep the phases lined up unless it is for balancing. I believe it has been in the Code for a very long time and the real reason by be lost. Perhaps someone else can shed some light on this question.

 

[don_resqcapt19]

I think I will submit a proposal requiring A,B,C to be clockwise rotation and see what the CMP does.

 

[crossman]

The second question is more complicated. We do indeed keep track of A?, B?, and C? from the substations so that we can balance the loads on the primary phases from the substation

Yes, that makes sense from the substations and a utility perspective. Thanks for making that point.

But as was mentioned, and just to press the point, the "A" phase originating on the secondary side of the final utility xfmr to the customer is completely arbitrary. (again, noting that the high leg delta will have one phase that is distinguishable from the other two.

If we have a wye secondary, the linemen can connect the line conductors to the service in any manner whatsoever, only the neutral need be determined. It may be clockwise, conunterclockwise, whatever. Any xfmr may be the "A" phase, any may be "B", etc. It is completely arbitrary.

Edit to add: So you build a new 3-phase wye service for a building. The poco shows up to connect it. I promise you that the linemen don't try to figure out which one of their xfmrs needs to be connected to your black wire, which xfmr to the red wire, which xfmr to the blue wire (or whatever colors you are using). They'll make sure their grounded conductor is the same as yours, but that is it. If you ask for a specific rotation, they may give it to ya, especially if it is a "service redo" to an existing building.

 

[crossman]

Standards in fabrication of Swgr,MCC,s etc is left to right A-B-C and front to back A-B-C. I have always applied that to what ever.

Yes, but from the secondary of the utility xfmr, A, B, and C are totally arbitrary. Is there anything specific about "A" phase that is different than "C" phase as registered on an oscilloscope? Before you say "yes, "A" phase will be 240 degrees ahead of "C" phase, well, that completely depends on how I connect the leads of the oscilloscope.

 

[crossman]

I read this as requiring a clockwise rotation when I hook my phase meter leads in the correct order from top to bottom or left to right.

I'm with charlie, I don't see that either. Why the bias and descrimination for clockwise? Why couldn't the ABC left to right mean counter-clockwise?

Edit to add: We used to do alot of service renovations such as adding xfer switches, generators, additions to switchboards for a major phone company. Before the utility cut the drops, we would take a rotation reading so that when it was time to reconnect the service, we could make sure the rotation was the same. I would guess that the clockwise services to counter-clockwise services was about 50/50.

 

[charlie]

Interesting proposal

Interesting proposal

I think I will submit a proposal requiring A,B,C to be clockwise rotation and see what the CMP does.

I would love to see the answer the panel makes.

 

[don_resqcapt19]

I'm with charlie, I don't see that either. Why the bias and descrimination for clockwise? Why couldn't the ABC left to right mean counter-clockwise?

Gary,
I'll ask you the same as I asked Charlie, if the A,B,C is not intended to reflect a rotation, what purpose do those code sections serve?

 

[crossman]

The only purpose those sections serve is that once you have established the phases for a particular system in your building, then you should continue that pattern throughout for that particular system. For example, you establish an arbitrary phase conductor to be "A" phase at the service disconnect. This same phase should be "A" on any sub-panels, disconnects, etc, on down the line., left to right, front to back.

But honestly, if my reasoning above is the purpose of the section, it is nonsensical anyway, IMHO. For what electrical purpose do the phases at a sub-panel need to be the same orientation as at the service? There is no electrical reason that I know of. (again, realizing that the high-leg, if it exists, is special)

For my money, I see no reason why the NEC would prefer clockwise over counter-clockwise. What makes a clockwise arrangement preferred over a counter-clockwise arrangement? What makes it a safer installation to have CW versus CCW?

 

[cadpoint]

The only purpose those sections serve is that once you have established the phases for a particular system in your building, then you should continue that pattern throughout for that particular system. For example, you establish an arbitrary phase conductor to be "A" phase at the service disconnect. This same phase should be "A" on any sub-panels, disconnects, etc, on down the line., left to right, front to back.

But honestly, if my reasoning above is the purpose of the section, it is nonsensical anyway, IMHO. For what electrical purpose do the phases at a sub-panel need to be the same orientation as at the service? There is no electrical reason that I know of. (again, realizing that the high-leg, if it exists, is special)

For my money, I see no reason why the NEC would prefer clockwise over counter-clockwise. What makes a clockwise arrangement preferred over a counter-clockwise arrangement? What makes it a safer installation to have CW versus CCW?

Why wouldn't the NEC state which way it's rotates, its on the load side of an install, A exhaust fan fins are built to exhaust not draw.
Theres some & other downline issues with some desired output of an installation.

 

[crossman]

Why wouldn't the NEC state which way it's rotates,

Why would it? And does the code mandate CW over CCW?

As for now, the NEC makes no mention of rotation, either CW or CCW. Why would the code prefer one over the other for safety purposes? Why is CW safer than CCW? (Read the next two paragraphs before answering)

its on the load side of an install, A exhaust fan fins are built to exhaust not draw.

It is possible, and probable, that I could show you two different exhaust fans from two different manufacturers, where I would have to swap the connections on the one and not swap them on the other to make them exhaust in the proper direction. The rotation of the fan would depend on the numbering of the motor leads, on the linkage from the motor to the fan, and even the manner in which the mounting orientation of the motor compared to the fan is.

Theres some & other downline issues with some desired output of an installation.

I can easily build two conveyor systems, using the same exact brand/type motor, where to make them both go in the desired direction for the manufacturing line, that I would have to swap the phases on one but not on the other.

The fact is, there is no way the NEC can mandate a rotation that must meet the ABC or L1L2L3 for motors throughout the entire system and have all motors going in the correct direction. It is, and has always been, a fact that the electrician (or someone) must check the direction of a 3-phase motor-driven equipment after it is installed to insure proper direction, and swap two leads if it is backwards.

 

[jeremysterling]

Here in Austin, there is a civic pride saying that goes, "Keep Austin Weird". I do not know if phase rotation is part of the city owned utility's quest for weirdness, but all installs are A-red, B-black, C-blue. High voltage is A-brown, B-yellow, C-purple.

I'm originally from Houston, which like most for the world follows the standard color code, so I'm still renumbering wirepulls from time to time.

Here is an excerpt from the POCO's website:

8.) Coordination and synchronization
The customer shall be solely responsible for coordination and synchronization of the customer's electrical generating system with all aspects of AE’s electrical system, and the customer assumes all responsibility for damage or loss that may occur from improper coordination and synchronization of its generating system with AE’s electrical system. The customer should be aware that the phase rotation used by Austin Energy is C-B-A.

 

[cadpoint]

Crossman, let me excuse myself, I got caught up in the conversation between You and the Thread, I'll stand with my statement just the same!

Motors can be wired as desired and the manufactures or my or Old Physic's Teacher could tell ya how to do it. They reflect that on the details of there label plate. Not that the say CW with its application!

Sorry maybe CW is what we can expect in Life.

 

[crossman]

but all installs are A-red, B-black, C-blue. High voltage is A-brown, B-yellow, C-purple. I'm originally from Houston, which like most for the world follows the standard color code, so I'm still renumbering wirepulls from time to time.

Well, there really is no "standard" color code. Houston ordinance is using Brown-Purple-Yellow-Gray for 480Y/277. Lots of places use Brown-Orange-Yellow-Gray for the same system. And you will find plenty of installations where the 480 is black-red-blue.

Here is an excerpt from the POCO's website:

8.) Coordination and synchronization
The customer shall be solely responsible for coordination and synchronization of the customer's electrical generating system with all aspects of AE?s electrical system, and the customer assumes all responsibility for damage or loss that may occur from improper coordination and synchronization of its generating system with AE?s electrical system.

That would have to be for an installation in which the customer equipment can provide more power than the customer is using, and the customer's equipment sends the excess back into the utility.

The customer should be aware that the phase rotation used by Austin Energy is C-B-A.

Lacking further info, that statment from the poco makes no sense whatsoever. Unless I have missed some IEEE standards or such, where does it say that ABC is CW? NESC? PoCo standards?

Again, what makes "C" phase from a generator "C" phase? Is there some characteristic of the "C" winding that makes it distinguishable from "A"? Or is it totally dependent on the person making the connections?

 

[dbuckley]

My point is, it is necessary to check the rotation of each motor upon installation, and swap two phases if backwards.

Absolutely, everywhere in the world.

Note that machine manufacturers will (in my experience anyway) ensure that all motors in the machine are wired with the same phase sequence order, so if one motor is correct, then all will be.

For the locals in 120V-land: UK three phase is just like straight 208/120, but 415/240 (well, in theory it should be 400/230, now the UK is EuroVolt), wye secondary, with the neutral bonded to earth / ground. The only thing you guys might notice as different is that the neutral / ground bond is almost always provided by the PoCo in their supplied equipment, so the electrician gets a feeder including ground.

The other thing you'll notice is no wild legs, corner grounds, or any other crazy scheme!

 

[crossman]

Crossman, let me excuse myself, I got caught up in the conversation between You and the Thread, I'll stand with my statement just the same!

Could you reiterate exactly what your statement was? I want to make sure I understand what you are saying.

Motors can be wired as desired and the manufactures or my or Old Physic's Teacher could tell ya how to do it. They reflect that on the details of there label plate. Not that the say CW with its application!

Sorry maybe CW is what we can expect in Life.

My point is, it is all arbitrary. Just because you have "ABC" CW at the service, and you take that "ABC" CW to a motor and connect A to T1 and B to T2 and C to T3, you will not necessarily get CW rotation of the motor. It totally depends on the labeling of the leads of T1, T2, and T3 from the manufacturer. Maybe there is a NEMA standard, but there is no law that all motors must conform to that standard. I can build a motor that will run exactly backwards from another motor, with the same connections from the service.